This invention relates to primer compositions and a method of employing the primer compositions to provide durably and tenaciously adhered abrasion resistant siloxane coatings on plastic surfaces. More particularly, this invention relates to primer compositions containing aminofunctional organosilicon compounds and thermosettable acrylic resins. In another aspect, the invention relates to a method of employing the primer compositions to improve the durability of the adhesion of abrasion resistant, colloidal silica filled siloxane coatings on plastic substrates.
Synthetic organic resins are well known materials that have many uses because of their ease of fabrication into desired shapes. One problem that has restricted the use of many resins is a lack of surface hardness and abrasion resistance. This problem is especially severe for resin applications in which transparency is required. In many cases, the rapid accumulation of minor abrasions and scratches on the surface can significantly reduce transparency and make an article essentially useless for its intended purpose.
To overcome this problem, colloidal silica filled organopolysiloxane coatings were developed to greatly improve the surface hardness of organic resins. Typical examples of these coatings are described in U.S. Pat. Nos. 3,986,997, 4,027,073 and 4,355,135. While these coatings have many excellent properties, they do not in all instances possess the desired degree of adhesion to resin surfaces. In particular, the durability of coating adhesion to substrates such as polycarbonate resin is often less than desired.
Methods of improving adhesion by priming the substrates prior to application of the siloxane coating are described in U.S. Pat. Nos. 4,207,357 and 4,284,685. These patents disclose the use of organic solvent solutions or emulsions of thermosettable acrylic resins for priming polycarbonate surfaces to improve adhesion of siloxane coatings. U.S. Pat. No. 4,242,381 further teaches that UV screens can be added to acrylic resin emulsion primers to protect the polycarbonate substrate from ultraviolet light.
Japanese Patent O.P.I. No. 92,742/80 teaches the addition of 3-aminopropyltriethoxysilane to acrylic paint to improve the adhesivity of the paint when it is applied to plastic articles previously coated with an abrasion resistant polysiloxane coating. Specifically, the silane modified acrylic paint is coated over the abrasion resistant polysiloxane coating.
Even though the acrylic resin primers taught by the art do improve adhesion, there is still a need in many instances for increased durability of adhesion. Thus, it is an object of the present invention to provide primer compositions that improve the durability of the adhesion of abrasion resistant polysiloxane coatings to plastic substrates. It is another object of the invention to provide a method of improving the durability of the adhesion of abrasion resistant polysiloxane coatings to plastic substrates. These and other objects of the invention will be apparent to one skilled in the art upon consideration of the following description and appended claims.